Before I answer your question, let me give you a friendly advice. Since you said you are "not too good at WordPress," please be very, very careful while editing the website code.
A single mistake might take the whole website down. If possible, get expert help in adding the code. Otherwise, take a complete backup of your site before making any changes.
Now that we are done with the warning, let's get to your question.
The end of the body tag will look like this:
And you will find the
</body> at the footer.php file of your active WordPress theme.
Let me know if you need any other help.